Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

737
FXUS63 KLOT 111956
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
156 PM CST Thu Dec 11 2025

.KEY MESSAGES...

- A period of accumulating snow this evening into tonight may
  lead to hazardous travel conditions southwest of a Peru, IL
  to Rensselaer, IN line.

- Another clipper system may produce a few inches of powdery
  snow accumulation in areas mainly south of Interstate 80 on
  Saturday.

- Very cold temperatures and bitterly cold wind chills are
  expected this weekend.

- There is a growing signal for a pattern change toward milder
  (and less snowy) conditions next week.

&&

.DISCUSSION...
Issued at 156 PM CST Thu Dec 11 2025

Through Friday:

The primary forecast focus continues to center on the next
quick moving clipper system expected to produce a 100 to 150
mile wide swath of accumulating snow across portions of the
region tonight. Forecast guidance, in conjunction with recent
regional radar and satellite observations, continue to focus
this swath of snow well southwest of the Chicago metro area,
roughly from southeastern IA southeastward through central IL
and southern IN. Across this region, a rather robust mesoscale
frontogenetic response is expected to develop for a few hour
period late this afternoon into this evening along the
tightening lower level baroclinic zone. This is likely to result
in an even narrower band of moderate to briefly heavy snow
rates (0.5 to 1" per hour) for a couple hours early this
evening. This will particularly be the case across central
portions of IL just to the southwest of my area where a Winter
Weather Advisory is in effect.

Snow rates outside of the main band will be much lighter
(generally a 0.5" or less per hour), particularly with
northeastward extent across LaSalle, Livingston, Ford and
Iroquois counties. In these areas, 1 to as much as 3" are
possible (highest in the southern portions of the counties).
Snow amounts will then tapper quickly with northeastward extent,
with little or no snow accumulation anticipated across most of
northeastern IL and far northwestern IN. Of the accumulations
that occur in my southwest counties, much of them will occur
this evening, with rates quickly tapering off overnight. Some
occasional flurries and/or light snow showers may persist across
portions of the area very into early Friday morning,
particularly near the IL Lake Michigan shore. However, lake
effect parameters are not expected to be overly impressive, so
little in the way of additional accumulation is anticipated.

Conditions on Friday will continue to be largely mostly cloudy.
Temperatures will also remain chilly, with highs generally in
the 20s to low 30s. Some occasional light snow or flurries may
also occur at times, particularly across northern IL during the
day as another weak impulse passes over WI. Little if any
accumulation is expected with this activity.

KJB


Friday Night through Thursday:

Cold front will move across the CWA Friday evening with much
colder air spilling south into the area in the wake of the
front. There could be a few flurries lingering into Friday
evening, but not looking for any organized or measurable
precipitation. Confidence in just how cold temperatures will get
Friday night is a bit on the lower end of the spectrum. NBM and
global guidance are quite cold with lows ranging from near 0
northwest CWA to around 10 southeast CWA. The heart of the
arctic air mass doesn`t look to arrive until later Sat or Sat
evening, so it`s plausible that those low temps are a bit too
cold. Didn`t make any changes to the NBM at this point since
even if the ambient temp is 4-5F warmer it is still going to
feel very cold and really won`t change the message.

An Alberta Clipper is progged to dive southeast into the Midwest
and phase with the tropospheric polar vortex over the Great
Lakes Saturday. Medium range guidance the past couple of days
has generally been on a gradual shift southward with the axis of
accumulating snow with this feature. Despite the trends in
GFS/GEFS and ECMWF/EPS, medium range guidance often struggles
with phasing and its quite plausible that there could still be
some sizable latitudinal changes in where the axis of
accumulating snow lays out Saturday. Current guidance would
favor our southern CWA south into central IL which is where NBM
has the highest pops and accums. Given the potential for this to
shift north or further south still, felt chance pops offered up
by the NBM up to the WI border looked reasonable.

Secondary push of arctic air is expected in the wake of that
clipper with the coldest air mass expected over the area
Saturday night into Sunday morning. Surface high looks to remain
well west of the region Saturday night, so despite clearing
skies, anticipate we`ll maintain some wind (10-15 mph). This
wind combined with what looks to be widespread subzero air temps
should push wind chills into the 15 to 25 below zero range
across the area.

Winds will gradually ease during the day Sunday and skies should
be clear, but only offering up deceptive sunshine as
temperatures should remain very cold. Many areas could struggle
to get out of the single digits above zero for highs. Even with
easing winds, wind chills during the day Sunday will probably
remain near or below zero.

Sunday night`s low temps are tricky and will likely depend
significantly on the exact location of the sfc high. If the high
is overhead or nearby, then a rapid evening temp drop to well
below zero could occur, however if the high is already moving
off to the east by evening, then developing southerly winds
could temper the evening temp fall. Guidance currently suggests
that the high will move well east of the area by early Monday
morning, so southerly winds should pick up overnight and result
in rising temps. The rise in temps will likely be partially
offset by the strengthening winds resulting in wind chills
remaining bitterly cold.

Medium range guidance continues to suggest a pattern change to a
more zonal flow across the country next week. This would tend to
keep the colder air bottled up to our north Canada with a return
to normal and probably eventually above normal temperatures.

- Izzi

&&

.AVIATION /18Z TAFS THROUGH 00Z SATURDAY/...
Issued at 1140 AM CST Thu Dec 11 2025

No significant weather is expected through the TAF cycle. MVFR
CIGS will likely continue through tonight and probably into
Friday as well. Confidence in MVFR CIGS lingering into Friday
is lower, as there is some potential to go VFR later tonight
into Friday. Any snow is expected to remain south of the the
terminals, though cannot rule out a few flurries tonight or
Friday afternoon. If they occur, any flurries would be unlikely
to result in any impacts to operations. Light winds are expected
through the period.

- Izzi

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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